Method of and smelter for producing steel with high manganese and low carbon content

ABSTRACT

A method of and a smelter for producing steel ( 1 ) with a high manganese and low carbon content on the basis of liquid pig iron ( 2 ) or liquid steel ( 3 ) and slag-forming constituents ( 4 ) with the object of preventing existing drawbacks of process route in vessels other than, e.g., electrical arc furnaces ( 18 ). With steel produced with a high manganese and low carbon content, in a process, the carbon component is reduced to about 0.7-0.8% by a combined blowing of oxygen ( 7 ) through top lances ( 8 ) and underbath nozzles ( 9 ) after feeding of liquid ferro-manganese (50 and liquid steel ( 3   a ) in a FeMn-refining converter (6 a ), wherein a component of a cold end product from premelt is added as cooling means ( 10 ), and wherein the carbon component is reduced to about 0.05-0.1% C by a continuous blowing of oxygen ( 7 ) through the underbath nozzles.

The invention relates to a method of and a smelter for producing steelwith a high manganese and low carbon content on the basis of liquid pigiron or liquid steel and slag-forming constituents.

Production of steel with a high manganese content in metallurgicalplants is carried out mainly on the basis of scrap in electrical arcfurnaces (Report at metallurgical Forum, Leoben 2003, authors Gigacher,Doppler, Bernard Krieger). During the production, a manganese carriersuch as ferro-alloy is added to the melt. This presents a problem asferro-manganese (FeMn) with a low carbon content is in about 300 timesmore expensive than similar products with a high C-content. FeMn with alow carbon content is, however, best suited for the production.

The production of steel with a high manganese content in a vessel otherthan electrical arc furnace fails because with blowing of oxygen, alarge amount of manganese slags as during decarburization of steel,oxygen develops a high affinity to manganese. Up to the present, withthe selection of the converter route, the drawback consisted in a highslagging of manganese and a correspondingly low manganese content insteel of about 16-17%.

The production of steel with a high manganese and low carbon content inelectrical arc furnaces is connected with several draw backs: inelectrical arc furnaces at temperatures up to 3000° C., a highvaporization of manganese takes place. Further, in order to insure a lowcontent of companion elements, a high-quality, expensive scrap isnecessary. Besides, use of the expensive ferro-alloys with a low carboncontent is necessary.

The object of the invention, is to eliminate the drawbacks of theproduction route in vessels other than electrical arc furnaces, and inwhich steel with a high manganese and low carbon content is to beachieved with the use of pig iron and liquid FeMn-charge.

The stated object is achieved, according to the invention, in that theprocess is carried out by feeding liquid ferro-manganese with about 6%of C and liquid steel with about 0.1% C, together with a necessaryamount of slag-forming constituents, in a FeMn-refining converter. Thecarbon component is reduced to about 0.7-0.8% by a combined blowing ofoxygen through top lances and underbath nozzles, thereafter, a componentof a cold end product from premelt is added as cooling means andthereafter, the carbon content is reduced to about 0.05-0.1% C by acontinuous blowing of oxygen through the underbath nozzles.

The working of the cooling means and the course of the combustionprocess of carbon at relatively low temperatures and beneath the bathlevel prevents evaporation of manganese. The use of FeMn carburizer as amanganese carrier insures an economical route for production of steelwith a high manganese content. The manganese content can be increased byabout 25-30%. The use of pig iron facilitates meeting of strictrequirements to content of copper and other companion elements. Theproduction of steel with a high manganese content with additives is alsopossible in an integrated steel plant. The addition of tramp elementsfrom scrap that contains, e.g., copper, zinc, tin, molybdenum, tungstenand the like, is not necessary.

Advantageously, a partial pressure is reduced by the combined blowing ofoxygen and an oxygen-inert gas mixture through the top lance or throughthe underbath nozzles.

In order to maintain advantageously, a low temperature, all of the stepsof the process is carried out in a temperature range between 1630-1650°C.

A further improvement of the method contemplates adding SiMn and or FeAlinto the melt in a ladle furnace for adjusting the analyses.

Thereby, steels such as TWIP-(Twinning Induced Plasticity) or TRIP(Transformation Induced Plasticity)-steel can be produced.

According to a practical embodiment, liquid FeMn75 carburizer in anamount of about 380 kg with 6% C (per ton of steel) and 530 kg of liquidsteel with 0.1% C and a necessary amount of slag-forming constituents isfed in a FeMn-refining converter, whereby the melt contains 23.3 kg ofcarbon that corresponds to a carbon content of C=2.6%. The carboncontent is reduced by a combined oxygen blowing over at least one toplance and a plurality of underbath nozzles, and finally, about 150 kg ofa cold end product from premelt is continuously added as cooling meansand the carbon content is reduced to about C=0.1% by blowing anoxygen—inert gas mixture through the underbath nozzles.

A smelter for producing steel with a high manganese and low carboncontent on the basis of liquid pig iron or liquid steel and slag-formingconstituents, is so formed that in a material flow, on one hand, areducing furnace or a blast furnace for pig iron and, on the other hand,a steel-smelting converter for carbon steel or an electrical are furnacearc furnace are arranged upstream of a FeMn-refining converter and, aladle furnace adjoins it in a process path.

The drawings show embodiments of the invention which will be explainedin detail below.

In the drawings:

FIG. 1 shows a diagram for a charging process (upper portion) and itscourse for decarburization process dependent on time (lower portion, and

FIG. 2 shows a block diagram with a routine of fed row material in asmelter.

According to FIG. 1, the process of producing steel 1 with a highcontent of manganese and a low content of carbon works on the basis ofliquid pig iron 2 or liquid steel 3 and slag-forming constituents 4 (seethe slag layer in FIG. 2). The process is initiated by introduction ofliquid ferro-manganese 5 with about 6% C and liquid steel or carbonsteel 3 a with about 0.1% C into a FeMn-refining converter 6 a with anecessary amount of the slag-forming constituents 4. Thereafter, thecarbon component is lowered to about 0.7 to 0.8% C by combined blowingof oxygen 7 with at least one top lance 8 and underbath nozzles 9.Simultaneously, a component of a cold product from a premelt is added ascooling means. In this phase, the carbon component reduction takes placeup to 0.05-0.1% C by continuous blowing in of oxygen 7 through underbathnozzles 9.

With a continuous blowing-in of oxygen 7 and an oxygen-inert gas mixture11 through the underbath nozzles 9 and the top lance 8, the partialpressure of oxygen in the melt can be reduced. All of the steps of theprocess take place in a (low) temperature range between 1630° C. and1650° C.

For adjusting the analysis in a ladle furnace, SiMn and/or FeAl are (is)added to the melt 13.

The smelter for producing steel 1 with a high content of manganese and alow content of carbon operates, according to FIG. 2, with pig iron orcarbon steel-supply 14, with addition of the slag-forming constituents 4and companion elements 15 of steel. To this end, a reducing furnace 16(with submerged electrodes), or a blast furnace 17 for pig iron 2, or asteel-smelting converter 6 for carbon steel 3 a, or an electrical arcfurnace 18, which are located, upstream, in the material flow, of aFeMn-refining converter 6 a, are used. A ladle furnace 12 adjoins theFeMn-refining converter 6 a.

According to a practical embodiment of the inventive process, in a firststep, a liquid carburizer FeMn 75 in an amount of about 380 kg with 6% C(per ton of steel), 530 kg of liquid steel with 0.1% C and a necessaryamount of slag-forming constituents 4 are loaded in the FeMn-refiningconverter 6 a, whereby the melt (13) contains 23.3 kg of carbon, whichcorresponds to carbon content of C=2.5%. In a second step, the carboncontent is reduced to about 0.7% by a combined oxygen blowing with atleast one top lance 8 and several underbath nozzles 9. In a third step,about 150 kg (to a ton of steel) of a cold end product from a premelt iscontinuously added as cooling means 10. In the fourth step, the carboncontent is reduced to about 0.1% C by delivering an oxygen-inert gasmixture 11 through the underbath nozzles 9 (the inert gas serves forprotection of nozzle and, simultaneously, functions as an agitator).

The adjustment of the analysis (TWIP or TRIP-steel) takes place byaddition of light metals (Si, Al, and the like), so that the desiredsteel 1 with a high manganese content and additives Al and Si can beproduced in an integrated steel plant.

REFERENCE NUMERALS

-   1 Steel with a high manganese content and a low C-content-   2 Liquid pig iron-   3 Liquid steel-   3 a Liquid carbon steel-   4 Slag-forming constituents-   5 Liquid ferro-manganese-   6 Steel smelting converter-   7 Oxygen-   8 Top lance-   9 Underbath nozzles-   10 Cooling means-   11 Oxygen-inert gas mixture-   12 Ladle furnace-   13 Melt-   14 Rig iron or carbon steel supply-   15 Companion elements-   16 Reducing furnace-   17 Blast furnace-   18 Electrical arc furnace

1. A method of producing steel (1) with a high manganese and low carboncontent on the basis of liquid pig iron (2) or liquid steel (3) andslag-forming constituents (4), characterized in that the process iscarried out by feeding liquid ferro-manganese (5) with about 6% of C andliquid steel (3; 3 a) with about 0.1% C, or liquid pig iron togetherwith a necessary amount of slag-forming constituents, in a FeMn-refiningconverter (6 a), the carbon component is reduced to about 0.7-0.8% by acombined blowing of oxygen (7) through a top lance (8) and underbathnozzles, thereafter, a component of a cold end product from premelt isadded as cooling means and thereafter, the carbon content is reduced toabout 0.05-0.1% C by a continuous blowing of oxygen (7) through theunderbath nozzles (9).
 2. A method according to claim 1, characterizedin that a partial pressure is reduced by the combined blowing of oxygen(7) and an oxygen-inert gas mixture (11) through the top lance (8) orthrough the underbath nozzles (9).
 3. A method according to claim 1,characterized in that all of the process steps are carried out in atemperature range between 1630-1650° C.
 4. A method according to claim1, characterized in that SiMn and/or FeAl is added to melt (13) in aladle furnace (12) for adjusting an analysis.
 5. (canceled)
 6. A smelterfor producing steel (1) with a high manganese and low carbon content onthe basis of liquid pig iron (2) or liquid steel (3) and slag-formingconstituents (4), characterized in that in a material flow, on one hand,a reducing furnace (16) for ferro-manganese and on the other hand, of ablast furnace (17) for pig iron (2) or a steel-smelting converter (6)for carbon steel (3 a) or an electrical arc furnace (18) are arrangedupstream of a FeMn-refining converter (6 a), and a ladle furnace (12)adjoins it in a process path.